This technology relates to a control device for electrically controlling a solenoid valve.
In automatic transmissions mounted, for example, on vehicles, shift speeds are achieved by forming transmission paths in accordance with the state of engagement of friction engagement elements, such as clutches and brakes. The state of engagement of the friction engagement elements is controlled by hydraulic pressure supplied to hydraulic servos thereof. The hydraulic pressure is commonly regulated by a linear solenoid valve provided in a hydraulic control device. The linear solenoid valve has a coil, and a current supplied to the coil drives a plunger (a movable iron piece) to control the position of a spool that regulates the hydraulic pressure, thus regulating the hydraulic pressure.
The current supplied to the linear solenoid valve is controlled by a control device (ECU). Specifically, the control device determines shifting on the basis of, for example, a vehicle speed and an accelerator operation amount, calculates a current value supplied to the linear solenoid valve on the basis of the determination, generates a PWM signal by PWM modulation of the current value, and controls an application voltage by driving switching elements with the PWM signal, thereby controlling the current flowing through the linear solenoid valve.
In the linear solenoid valve described above, when the current flowing through the coil reaches a steady state, the plunger and the spool become stationary accordingly. When the current is changed in order to move the spool, especially after a sliding friction is exerted by the coefficient of static friction on the spool, a delay in response may occur, and hydraulic responsiveness may become degraded. In a known approach to preventing the stationary state so as to improve the hydraulic responsiveness, the current is periodically oscillated with a dither period, i.e., the position of the spool is oscillated with the dither period (refer to Japanese Patent Application Publication No. 2014-197655).